Acetabular component orientation in intra- and postoperative positions in total hip arthroplasty

In total hip arthroplasty (THA), acetabular component orientation has critically important effects on dislocation, range of motion, polyethylene wear, pelvic osteolysis, and component migration. The differences in the pelvic orientation in the intraoperative lateral position for insertion of acetabular component during operation and that in the postoperative supine position for evaluation of acetabular component orientation will be one of the factors, which make outliers in acetabular component orientation. We compared acetabular component orientation between intraoperative lateral position and postoperative supine position in 100 consecutive primary THAs. A total of 100 consecutive primary THAs (between October 2004 and December 2005) in 100 patients performed by a single surgical team were investigated. Intraoperative anteroposterior radiographs of pelvis in the lateral position and postoperative anteroposterior radiographs of pelvis in the supine position were taken. Acetabular component orientation (vertical tilt and anteversion) were measured using computer software. The absolute values of difference between measurements in the two positions were 5.3A degrees A A +/- A 4.5A degrees (mean +/- A SD) for vertical tilt and 5.1A degrees A A +/- A 3.7A degrees for anteversion. The difference in the vertical tilt between the two positions was significant (P < 0.0001). The difference in the acetabular component orientation between the two positions, which might be caused by the difference between intra- and postoperative pelvic orientation, should be considered during THA.